The present invention relates to a sputtering target-backing plate assembly comprising characteristics that are required in magnetron sputtering.
Conventionally, the sputtering method capable of easily controlling the film thickness and components has been broadly used as one type of deposition method of materials for electronic/electric components. Moreover, in order to increase the sputtering deposition rate, a magnetron sputtering device, which controls the plasma based on electromagnetic force, has been broadly used in particular. Moreover, while the power input to the sputtering target is being increased as much as possible in order to increase the deposition rate, in the foregoing case, the sputtering target is heated from the collision of positive ions with the target surface, and the temperature of the target tends to increase together with the increase of the input power.
Normally, a sputtering target is bonded with a backing plate that is prepared from a material having favorable thermal conductivity such as copper, and this backing plate is configured to be cooled via means such as water-cooling so as to indirectly cool the sputtering target that is heated as described above. Since the backing plate is recycled in many cases, the sputtering target and the backing plate are often bonded with a brazing material or adhesive so as to enable the replacement of the sputtering target.
Generally speaking, a magnet in the magnetron sputtering device adopts a structure of being rotated in a cooling device. In this kind of device, an eddy current is generated when the magnet is rotated in the cooling device, and the eddy current increases together with the increase in the speed of rotation. In addition, a reverse magnetic field is generated due to the eddy current, and the generated reverse magnetic field functions to reduce the equivalent magnetic flux. The reduction of the equivalent magnetic flux consequently affects the uniformity of the film significantly, and there is a problem in that the deposition rate will fluctuate.
Conventional technologies are introduced below.
Patent Document 1 discloses a copper or copper alloy target-copper alloy backing plate assembly for use in magnetron sputtering, wherein the copper alloy backing plate is made from a beryllium copper alloy or a Cu—Ni—Si alloy.
Moreover, Patent Document 2 describes an assembly obtained by bonding a sputtering target made from copper, aluminum, tantalum or the like, and a backing plate made from a copper alloy or an aluminum alloy having a specific resistance value of 3.0 μΩ·cm or more, and a tensile strength of 150 MPa or more.
Patent Document 3 discloses an assembly configured by bonding a backing plate for sputtering made from a Cu alloy having a 0.2% proof stress of 200 MPa or more, and a sputtering target. Moreover, Patent Document 4 describes an assembly configured by bonding a backing plate for sputtering made from an Al alloy having a 0.2% proof stress of 200 MPa or more, and a sputtering target.
Patent Document 5 discloses an assembly configured by diffusion-bonding the target and the backing plate via an insert material made from aluminum or an aluminum alloy and in which the deformation after diffusion bonding is small even when the difference in the thermal expansion rate between the target and the backing plate is great. Moreover, Patent Document 6 describes a sputtering target-backing plate assembly having a structure in which pure copper is embedded in the backing plate position at the center of the target and which yields superior strength and eddy current characteristics.
Nevertheless, the conventional sputtering target-backing plate assemblies faced the following problems. In other words, since the sputtering target becomes heated in accordance with the input power (sputtering power), the heating and cooling of the target is repeated when the sputtering source is turned ON and OFF. Thus, the sputtering target-backing plate assembly is subject to plastic deformation as a result of repeating the deformation caused by the thermal expansion and contraction as a bimetal as shown in FIG. 1. In addition, this kind of deformation of the target caused the problems of inducing changes in the uniformity of the film thickness and the deposition rate, coming into contact with the magnet and so on.